Share-based Compensation (Nonvested Options) (Details) - Nonvested Option Shares - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Nonvested Awards, Number of Shares [Roll Forward]
Nonvested awards, Shares, beginning balance	74,625	75,750	67,500
Nonvested options, Granted	42,000	42,000	42,000
Nonvested options, Vested	(40,125)	(43,125)	(33,750)
Nonvested options, Canceled	0	0	0
Nonvested awards, Shares, ending balance	76,500	74,625	75,750
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Exercise Price [Roll Forward]
Nonvested options, Weighted Average Exercise Price, beginning balance (in dollars per share)	$ 36.35	$ 19.27	$ 16.52
Nonvested options, Granted, Weighted Average Exercise Price (in dollars per share)	53.90	49.22	22.25
Nonvested options, Vested, Weighted Average Exercise Price (in dollars per share)	32.54	18.89	17.47
Nonvested options, Canceled, Weighted Average Exercise Price (in dollars per share)	0.00	0.00	0.00
Nonvested options, Weighted Average Exercise Price, ending balance (in dollars per share)	$ 47.99	$ 36.35	$ 19.27